1. Field of the Invention
The present invention relates to an electrically controlled pressure accumulating distribution type fuel injection pump for supplying high-pressured fuel accumulated in a pressure accumulation chamber is distributed to each cylinder and supplied.
2. Background Art
In recent years, under the tendency that a regulation on an exhaust emission becomes strict, a diesel engine is desired so as to reduce NOx and particles or the like in exhaust gas while having low fuel economy. In order to cope with this problem, a fuel injection pressure is heightened so as to improve fuel efficiency.
Then, there is increasing an electrically controlled pressure accumulation style fuel injection pump that can arbitrarily control its injection pressure irrespective of the rotary speed of the engine while enabling the fuel injection pressure to be heightened.
This kind of pressure accumulating fuel injection type fuel injection pump aims at supplying high-pressure fuel accumulated in its pressure accumulation chamber to each cylinder, as is described, for example, in Japanese Unexamined Patent Publication No. HEI 7-509042.
The pressure accumulating fuel injection pump comprises a fuel pressure accumulation chamber, a plunger for pressure-supplying high-pressure fuel, an injection control valve for fuel injection control, distribution means for distributing fuel to each cylinder, and a pressure control valve. They serve as function members constituting a high-pressure path to which a high pressure is applied at all times. These function members are separated and accommodated in respective casings or blocks formed separately from one another.
In this manner, since the high-pressure is also applied to connection portions among such separately structured function members, the strength thereof is hard to be secured. In some cases, fuel leakage and damage are likely to be generated therefrom, thereby lowering their reliability. Also, their structures are complicated.
Furthermore, the pressure accumulating fuel injection pump is provided with a plurality of plunger chambers for pressure-supplying fuel to the pressure accumulation chamber. Since the plurality of plunger portions are juxtaposed in the direction of a camshaft, the pressure accumulation fuel injection pump becomes large and complicated.
The present invention provides a pressure accumulating distribution type fuel injection pump for distributing and supplying high-pressure fuel accumulated in one or a plurality of pressure accumulation chambers thereof to each cylinder through its distribution means, wherein function members constituting a highpressure path are arranged in a hydraulic base. The function members include a plunger, a pressure control valve, a fuel injection control valve, the pressure accumulation chamber or chambers, and distribution means. As a consequence, the strength of these constituent members for the high pressure path arranged together in the hydraulic base can be sufficiently secured while a high pressure is applied thereto at all times. Furthermore, the constituent members can be connected with one another through hydraulic channels constituted of drill holes or the like formed in the hydraulic base without joint members or the like so that fuel leakage and damage on the piping are not generated, thereby improving reliability.
Furthermore, the present invention is such that a distribution shaft serving as the distribution means is arranged perpendicularly to a camshaft. As a consequence, the size of the fuel injection pump can be reduced in the direction of the camshaft. Furthermore, In a small-size engine, delivery valve holders can project upwardly so as to shorten delivery pipes extended therefrom to respective injection nozzles. Consequently, the fuel volume in the injection pipes decreases so as to make the injection delay smaller, thereby enabling the injection ratio and period to be controlled in a high precision over a wide scope of rotation.
Furthermore, the present invention is such that the camshaft for driving the plunger also drives the distribution shaft. As a consequence, the fuel passage which reaches the delivery valves through the distribution shaft from the plunger portion is shortened so as to decrease the fuel volume therein, thereby heightening the quality of injection control such as ratio and period controlling of minute quantities of pilot and post injections, initial injection and so on.
Furthermore, the present invention is such that one plunger portion is provided for pressure accumulating fuel to the pressure accumulation chamber or chambers. As a consequence, the fuel injection pump can be reduced in size, and the number of parts can be reduced, thereby facilitating the manufacture and saving costs thereof.
Furthermore, the present invention is such that a cam for driving the plunger in the plunger portion is formed separately from the camshaft. Particularly if the fuel injection pump is formed for multiple cylinders, while the cam, which abuts against a tappet under high surface pressure because the curvature of its surface in contact with the tappet becomes small, is made of high surface-pressure proof material such as SKH, SKD or ceramic so as to be heightened in its endurance against friction, the camshaft can be formed of material whose strength is reduced in comparison with the material of the cam, thereby saving costs.
Furthermore, the present invention is such that a pulse generator for differentiating cylinders is provided on the camshaft of the above-mentioned pressure accumulating distribution type fuel injection pump and is integrally formed with the cam. Such a combination of parts can effect to reduce the number of parts, thereby reducing the manufacturing cost and size of the fuel injection pump.
Furthermore, the present invention is such that the rotary speed of the camshaft for driving the plunger for pressure-supplying fuel to the pressure accumulation chamber or chambers is set to the same as the output rotary speed of the engine on which the pressure accumulating distribution type fuel injection pump is attached, and the rotary speed of the distribution means is set to a half of the output rotary speed of the engine. As a consequence, for example, in the case of a four-cycle engine, the number of the cam projections can be reduced to a half of that of cylinders, thereby reducing the size of the cam and the number of steps for processing the cam.
Also, the cam profile can be reduced to half speed and their external peripheral surface can be formed into convex so that the cam can be easily ground by a diametrically large grindstone, thereby reducing the time and cost for processing the cam.
Furthermore, the present invention is such that the camshaft drives the distribution means via bevel gears, and the gear teeth of the bevel gear on the side of the distribution means are set to be twice as many as the gear teeth of the other gear on the side of the camshaft. As a consequence, with a simple structure and at a low cost, the rotary speed of the distribution means can be set to a half of the rotary speed of the camshaft.
Furthermore, the present invention is such that, while both end portions of the camshaft are supported by supporting portions of a housing, a bearing for supporting the peripheral surface of the camshaft opposite to the plunger is shifted from the supporting portions of the housing toward the center of the camshaft so as to be arranged in the vicinity of the cam. As a consequence, the load which the camshaft receives from the plunger or the like can be received with the bearing thereby making it possible to suppress a warp of the camshaft and reduce the vibration and noise. Besides, the size of the bevel gear can be formed in a small size, and the fuel injection pump can be reduced in size on the whole.
Furthermore, the present invention is such that the pressure control valve and the injection control valve for the pressure accumulation of the plunger portion, which are function members of the control system, are respectively arranged perpendicularly to the camshaft, thereby reducing the size of the fuel injection pump in the direction of the camshaft so as to minimize the whole of the fuel injection pump. Besides, if the camshaft is arranged horizontally, the axes of the pressure control valve and the injection control valve become vertical so as to prevent their slipping portions from eccentric friction.
Furthermore, the present invention is such that the pressure control valve for pressure accumulation of the plunger portion, the distribution means, and the injection control valve, which are function members of the control system are arranged perpendicularly to the camshaft respectively. As a consequence, the size of the fuel injection pump in the direction of the camshaft can be reduced, so that the whole size of the fuel injection pump can be reduced. Furthermore, if the camshaft is arranged horizontally, the axes of the pressure control valve for pressure accumulation, the distribution means and the injection control valve become vertical so as to prevent their slipping portions from eccentric friction.
Furthermore, the present invention is such that the above-mentioned function members of the control system are aligned in the direction of the camshaft in the order of the plunger portion, distribution means, and injection control valve. As a consequence, the size of the fuel injection pump in the direction of the camshaft can be reduced so as to reduce the whole size of the fuel injection pump.
Furthermore, the present invention is such that the plunger portion for pressure accumulation, the distribution means, and the injection control valve are arranged in series. As a consequence, the size of the fuel injection pump in the direction of the camshaft can be reduced so as to reduce the whole size of the fuel injection pump.
Furthermore, the present invention is such that the electromagnetic valve for pressure control of the plunger portion is arranged at an end portion of the plunger, and the electromagnetic valve for control of the injection control valve is arranged at the end portion of the injection control valve. As a consequence, the size of the fuel injection pump in the direction of the camshaft can be reduced so as to reduce the whole size of the fuel injection pump.
Furthermore, the present invention is such that the slide directions of the slide members of the electromagnetic control valves are set to be perpendicular to the camshaft. Each kind of the electromagnetic valves, which is only one irrespective of the number of cylinders, must be operated at the number of the cylinders every one rotation of the camshaft so that its operation is required to be extremely rapid and frequent, and furthermore, to be high-precision and harsh for controlling the quantity and period of injection to high-precision. However, the electro-magnetic control valves can be prevented from generation of eccentric friction on their slide portions during their rapid and frequent operations so as to improve their endurance and reliability because valve bodies serving as slide members of the electric-magnetic control valves are arranged so as to slide substantially perpendicular to the axis of the camshaft.
Furthermore, the present invention is such that a plurality of pressure accumulation chambers are arranged in parallel to each other. As a consequence, the oil passages connecting the respective pressure accumulation chambers with the plunger chamber for detaining fuel to be pressure-supplied by the plunger can be shortened, thereby reducing a surplus volume of the fuel passage, the term of fuel pressure-supplying and the power loss.